A conventional hydraulic shock absorber described in patent document 1 is structured, as shown in FIG. 7, such that a piston rod 2 which is attached to one of a vehicle body side and an axle side is inserted into an oil chamber of a cylinder 1 which is attached to another of the vehicle body side and the axle side. The oil chamber of the cylinder 1 is divided into a piston side oil chamber 4A and a rod side oil chamber 4B by a piston 3 which is provided in a leading end portion of the piston rod 2, and a damping force generating device 5 is provided in the piston 3. Further, an oil reservoir chamber 6 which compensates a volumetric capacity (including a volumetric capacity at a temperature expanding amount of an oil) of the piston rod 2 which goes to and out of the oil chambers 4A and 4B of the cylinder 1 is communicated with the piston side oil chamber 4A of the cylinder 1. And a valve housing 7 provided with a damping force generating device 8 is interposed between the piston side oil chamber 4A of the cylinder 1 and the oil reservoir chamber 6. The oil reservoir chamber 6 is pressurized by an air chamber 6A (a bladder, a free piston or the like may be interposed between the oil reservoir chamber 6 and the air chamber 6A).
The damping force generating device 5 is constructed by a compression side damping valve 5A which opens and closes a compression side flow path 3A provided in the piston 3, and an extension side damping valve 5B which opens and closes an extension side flow path 3B provided in the piston 3. The damping force generating device 8 is constructed by a compression side damping valve 8A which opens and closes a compression side flow path 7A provided in the valve housing 7, and an extension side damping valve 8B which opens and closes an extension side flow path 7B provided in the valve housing 7.
In a compression side stroke, oil in the piston side oil chamber 4A is boosted so as to flow out to the oil reservoir chamber 6 from the compression side damping valve 8A of the compression side flow path 7A and flow out to the rod side oil chamber 4B from the compression side damping valve 5A of the compression side flow path 3A, thereby generating a compression side damping force on the basis of a flow path resistance of the compression side damping valve 8A and the compression side damping valve 5A. At this time, the oil at an inserting volume of the piston rod 2 is discharged to the oil reservoir chamber 6 through the compression side damping valve 8A. In an extension side stroke, the oil in the rod side oil chamber 4B is boosted so as to flow out to the piston side oil chamber 4A from the extension side damping valve 5B of the extension side flow path 3B, thereby generating an extension side damping force on the basis of a flow path resistance of the extension side damping valve 5B, and the oil at a going-out volume of the piston rod 2 is replenished to the piston side oil chamber 4A from the oil reservoir chamber 6 through the extension side damping valve 8B of the extension side flow path 7B.